1. Field of the Invention
The present invention relates generally to a document scanner having a back light for scanning a transmissive document, and in particular to a scanner having a layer of fluorescent material on the back side of the transmissive document to generate a back light.
2. Description of the Prior Art
A scanner is widely used in office automation to scan pictures, documents, and many other images. The document scanners are generally categorized as (1) reflective type for scanning documents printed on non-transmissive media and (2) transmissive type for scanning documents printed on transmissive media.
FIG. 1 of the attached drawings shows a typical reflective type document scanner, which comprises a casing 1 having a top wall 11 mounted with a light-transmittable document supporting plate 12 for supporting a reflective type document 10 to be scanned. A top cover 13 is pivoted to the casing 1 for covering the document 10 positioned on the light-transmittable document supporting plate 12. A light-blocking layer 131, which is often white, is formed on an underside surface of the top cover 13.
Also referring to FIG. 2, the conventional reflective type scanner comprises an optic module 14, which comprises a light source 16 projecting a scanning light toward the document 10 and a number of reflective mirrors 171–174 which form a light path for the reflected scanning light. A focusing lens 18 focuses the reflected light to an image sensing unit 19, such as a Charge Coupling Device (CCD) whereby the image printed on the document 10 is read by the image sensing unit 19. The optic module 14 is movable in direction I along a pair of rails 15a, 15b fixed inside the casing 1 for scanning the whole surface of the document 10.
FIG. 3 of the attached drawings shows a typical transmissive scanner, which comprises a casing 2 having a top wall 21 provided with a light-transmittable document supporting plate 22 for supporting a transmissive document 20 thereon. A back light module 23 is pivotally mounted on the casing 2. With reference to FIG. 4, a back light source 26 is arranged in the back light module 23 and a light-transmittable window 231 is formed on an underside surface of the back light module 23. The back light source 26 projects a scanning light, via the light-transmittable window 231, through the transmissive document 20.
The conventional transmissive scanner also comprises an optic module 24 arranged inside the casing 2. The optic module 24 comprises a number of reflective mirrors 271, 272, 273 for guiding the scanning light that transmits through the transmissive document 20 toward a focusing lens 28. The focusing lens 28 focuses the scanning light onto an image sensing unit 29, such as a Charge Coupling Device. The optic module 24 is movable in direction I along rails 25a, 25b for scanning the whole surface of the transmissive document 20.
The conventional scanners as described above can only perform scanning operation on either the transmissive documents or non-transmissive documents. Heretofore, no scanner is capable to perform scanning operation on both transmissive and non-transmissive documents. Although it is obvious to those having ordinary skills to provide a back light module to a reflective type scanner for performing a transmissive type scanning operation, the addition of the back light module inevitably increases the overall size of the reflective type scanner. Furthermore, in performing the transmissive type scanning operation, the back light source must move in synchronization with the optic module. This complicates the structure and mechanism of the scanner.
It is thus desired to provide a document scanner for overcoming the above problems.